A single-phase induction motor comprises a first winding and a second winding, these two windings presenting a common point linking one end of each winding. The other end of the first winding is linked to the first phase terminal and the other end of the second winding is linked to the second phase terminal. A motor capacitor CM is disposed between these two other ends. Thus, depending on whether a voltage is applied between the first phase terminal and the common point or between the second phase terminal and the common point, either the capacitor is placed in series with the second winding and the motor rotates in a first direction, or the capacitor is placed in series with the first winding and the motor rotates in a second direction. The winding that is in series with the capacitor is qualified as auxiliary and the other is then qualified as main.
A first problem arises with such an actuator when it comprises a single controlled switch, the latter being disposed on the neutral conductor and being used in particular to automatically cut off the motor power supply when an obstacle is detected or when a particular position is reached. In practice, when this switch is open, the voltage at the terminals of the motor capacitor is zero since no current is flowing in the auxiliary winding. The second phase terminal then takes a potential equal to that of the first phase terminal when the switch controlling the motor links the phase of the mains to the first terminal P1. It is therefore not possible to identify the nature of the control command applied.
This can seem to have no effect: however, when the controlled switch is closed, the motor necessarily rotates in the direction imposed by the position of the control switch. In practice, if the motor is fitted with a load detection system (for example, by analyzing the motor torque), it is important for the control electronics of the motor to recognize the control command applied in order to choose accordingly the control thresholds or algorithms. In practice, these thresholds or algorithms can differ depending on whether the load is driven (for example, the raising of a roller blind) or driving (for example, the lowering of a roller blind).
A second problem arises when this controlled switch is closed: when the motor is powered in a direction, it is essential to be able to identify an abrupt operation of the control switch from the first position to the second position. Such a reversal of the power supply leads to both a major overcurrent and a mechanical jolt provoking premature wear of the components.